This invention relates generally to a sootblower device for directing a fluid spray against a heat exchanger surface for cleaning the heat exchanger surface and in particular to a sootblower device having a drain for return of a portion of the fluid medium from the lance tube which is selectively controllable to regulate the flow of the fluid against the heat exchanger surface.
Cleaning highly heated surfaces, such as the surfaces of a boiler, furnace, incinerators or the like used to extract heat, has commonly been performed by devices generally known as sootblowers. Sootblowers typically employ water, steam, air or a combination thereof as a blowing medium which is directed through one or more nozzles against encrustations of slag, ash, scale and/or other foul materials which become deposited on the heat exchanger surfaces. Throughout the specification claims, the term "heat exchanger" is broadly used to refer to boilers, furnaces, incinerators or the like having internal surfaces in need of periodic cleaning to remove encrustations.
It is known that water in liquid form, either used alone or in combination with a gaseous blowing medium, increases the ease with which the encrustations are dislodged. The effectiveness of water in dislodging the encrustations results from a thermal shock effect coupled with mechanical impact. The thermal shock shrinks and embrittles the encrustations resulting in a fracturing of the encrustations so that they become dislodged and fall away from the heat exchanger surfaces because of the mechanical impact.
Various types of sootblowers have been developed for cleaning heat exchanger surfaces One type of sootblower is known as the retracting variety which employs a lance tube that is advanced into a heat exchange through a wall port. The lance tube has one or more nozzles through which the cleaning or blowing medium is discharged and sprayed against the heat exchanger surfaces. After a cleaning cycle has been completed the lance tube is retracted from the heat exchange until cleaning is again needed. During each cleaning cycle, in addition to being advanced and retracted into and from the boiler, the lance tube is often rotated so that the spray of blowing medium is directed along a spiral path against the heat exchanger surfaces. Retractable sootblowers are used in applications where the internal temperatures of the heat exchanger are sufficient to damage the lance tube and shorten its life if permanently installed in the heat exchanger. Other sootblowers employ a permanently positioned lance tubes which, during each cleaning cycle may be rotated or rotationally oscillated back and forth to move the jet stream of the blowing medium.
Unfortunately, to obtain sufficient cleaning with the water spray process mentioned above, a danger of over stressing the hot heat exchanger surfaces is present. Rapid deterioration of the heat exchanger surfaces as a result of thermal shock from the cleaning process has been observed. The problem of heat exchanger surface deterioration has been particularly severe in connection with cleaning the rigidly held tube bundles of large scale boilers. Being rigidly held, the tubes can not readily distort in response to the temperature induced shrinkage and expansion occurring during a cleaning cycle. The potential for damage to the heat exchanger surfaces is greater if the blowing medium is sprayed against a surface a second time, after it has been recently cleaned, where the blowing medium contacts the surface directly rather than contacting an encrustation on the surface. Such multiple cleanings of a surface can occur where the jet stream from two sootblowers overlap one another. As a result, it is desirable to periodically, during a cleaning cycle, terminate the flow of the blow medium from the sootblower where the jet stream will cover a previously cleaned surface.
During certain portions of the lance tube rotation during a cleaning cycle, the jet stream will not be directed toward a heat exchanger surface in need of cleaning. It is also desirable to stop the flow of the blowing medium to avoid the needless discharge into the heat exchanger which places a thermal load on the heat exchanger and also wastes the blowing medium.
However, in terminating or reducing the flow of the blowing medium, it is not always possible or practical to entirely eliminate the flow of the blowing medium. For example, it may be necessary to maintain a minimum flow rate through the lance tube in order to provide cooling of the lance tube within the heat exchanger.
Accordingly, it is an object of the present invention to provide a means for regulating the flow of the blowing medium from the lance tube into the heat exchanger during each cleaning cycle depending on the position of the lance tube nozzles.
It is a feature of the present invention to provide the sootblower with a drain for returning a portion of the blowing medium from the lance tube for disposal outside of the heat exchanger so that excess blowing medium is not discharged into the heat exchange. This returned cleaning medium can be reused or discarded.
In one embodiment of the invention, the lance tube is equipped with an inner tube extending therein creating an inner passage within the inner tube and an outer passage between the inner tube and the inner surface of the lance tube. The outer passage is used for supplying the blowing medium to the lance tube while the inner passage is used for return of a portion of the blowing medium for discarding externally of the heat exchanger. By opening the return flow path, the flow of the blowing medium through the lance tube nozzles is controllable based on the relative restriction to flow of the blowing medium through the nozzle as compared to the return flow path. When it is desirable to terminate or at least reduce the flow of the blowing medium through the lance tube nozzles, the supply of blowing medium can be reduced to a minimum value necessary for cooling and other purposes. However, to further reduce the discharge of blowing medium through the nozzle, the return flow path is open whereby only a portion of the blowing medium used for cooling, etc. is discharged through the nozzles and into the heat exchanger. The remainder is discarded externally of the heat exchanger.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.